The militant group blamed for the Mumbai attacks has roots in the disputed Kashmir region where Pakistan's military has faced off against India for decades.
There have long been suspicions that Pakistan's military and intelligence services helped create, arm and train Lashkar-e-Taiba as a proxy force against India's much larger military.
Though ties between the militant group and Pakistan's army have never been firmly established, the issue is coming under fresh scrutiny and could determine India's response to the terror attacks.
Pakistan has repeatedly denied any connection to the group.
Any evidence linking the Mumbai attackers to the Pakistani leadership would raise tensions between the nuclear-armed neighbors after years of attempts to mend relations. In a worst-case scenario, it could push India's government to mobilize troops along the border or even bomb militant targets within Pakistan.
The only surviving gunman told police he is Pakistani and trained at a Lashkar camp in Pakistan, according to Indian security officials; Indian leaders have also blamed "elements within Pakistan" for the strikes.
The Islamabad government acknowledges the attackers may be Pakistani or may even have trained on its soil, but insists they did so without its knowledge. Government leaders have also repeatedly noted they too are fighting a bloody war against Islamic militants.
The Pakistani government banned Lashkar in 2002 amid pressure from Washington following the Sept. 11 attacks. Since then most analysts say infiltration by militants into Indian-held Kashmir has decreased.
But a senior Pakistani government official acknowledged individuals among the lower-ranks of the intelligence agencies may sympathize with groups like Lashkar, which has been linked to al-Qaida and whose members are believed to be involved in attacks against the government and army close to the Afghan border.
"Maybe one or two individuals are allowing things to happen," but there is no officially sanctioned connection to the militants, said the official, who asked not to be identified because it would compromise his work.
The situation is further muddied because many people question whether Pakistan's civilian government, which was elected in February ending nine years of military rule, is in full control of the army and intelligence agencies.
Relations between the military government under President Gen. Pervez Musharraf and jihadi groups deteriorated following the July 2007 assault on the Red Mosque in Islamabad, which left scores of militants dead. The mosque was historically used as a jumping off point for militants en route to the fight in Kashmir.
Hundreds of Pakistani soldiers have died in a spike in suicide bombings since the mosque assault. A Pakistani army operation in the Bajur border region that began in September has also targeted militant hideouts, some of them belonging to Lashkar-e-Taiba, according to military officials in the area.
But defense analyst Aysha Siddiqa said it appears the military still tolerates Lashkar and a related group, Jaish-e-Mohammed, especially in southern Punjab province, where both groups have their base.
"You could argue rogue elements are involved, but in Bahawalpur (in southern Punjab) you have the presence of an army corps," said Siddiqi. "If they can't pick up that there is something going on among the jihadi groups and stop them, then there must be something. Of course the links are still there."
On terrorism blacklist
India has accused Lashkar-e-Taiba of other attacks on Indian targets in recent years, including the 2001 attacks on parliament in New Delhi and train bombings that killed 180 in Mumbai in 2006.
The United States and Britain listed it as a terrorist group in 2001.
After Pakistan banned the group in 2002, Lashkar-e-Taiba, which means the Army of the Pure, is believed to have resurfaced under a new name, Jamaat-ud-Dawa, according to the U.S. and intelligence experts.
Jamaat-ud-Dawa says it focuses on charity work and publicly insists it has no links to Lashkar, which it says operates only in Kashmir, where an Islamic separatist insurgency against Indian rule has left more than 60,000 people dead since 1989.
Militant groups such as Lashkar want a Kashmiri merger with Pakistan, as Islamabad is also demanding. Some separatist groups want independence from both countries.
Many of the early militants in Kashmir had roots in the 1980s war in neighboring Afghanistan, when the United States and Saudi Arabia trained tens of thousands of young jihadis to fight the Soviet occupation. After the Soviet pullout in 1989, many of the Pakistani militants were redirected to fight Indian soldiers in Kashmir.
In the 1990s, the United States threatened to declare Pakistan a terrorist state because of its military and intelligence links to jihadi groups in Kashmir, including Lashkar-e-Taiba.
Lashkar and Jaish-e-Mohammed established training camps in Afghanistan during the Taliban regime, and were closely aligned to al-Qaida operatives there. Several senior Jaish-e-Mohammed operatives were close to al-Qaida leader Osama bin Laden. Masood Azhar, the group's leader, was one of three prisoners released by India to put an end to the December 1999 hijacking of an Indian Airlines aircraft in Kandahar, Afghanistan.
In the U.S., one of the largest terror prosecutions since 2001 involved a group of young Muslim men from the Washington, D.C., area who trained at Lashkar camps in Pakistan, and who used paintball games in the Virginia woods as a way of preparing for global holy war.
Most members of the so-called "Virginia jihad network" never intended to stay with Lashkar, but viewed training with the group as a gateway for joining the Taliban or fighting in Chechnya, Afghanistan and other hotspots.
David Laufman, a former assistant U.S. attorney who prosecuted some of the cases, said he remains wary of reports implicating Lashkar in the Mumbai attacks, saying it would "demonstrate a major improvement in their ability ... to plan and execute attacks on this scale."
Pattern of similarities
However, a U.S. counterterrorism official said Monday that the small arms and explosives tactics used in the Mumbai assault were typical of Lashkar militants. "This is not outside the pattern they've used in the past," said the official, who spoke on condition of anonymity in discussing sensitive foreign intelligence.
He noted that Lashkar has a social services arm, which embeds it in communities and makes it harder to combat.
Jamaat-ud-Dawa is run by Hafiz Saeed, who used to head Lashkar. After the devastating earthquake in October 2005, the group set up camps throughout Pakistani Kashmir, the region hardest hit by the quake that killed 71,000 people. At the time, residents readily acknowledged that Janaat-ud-Dawad was the successor to Lashkar-e-Taiba.